BB Beeesssttt MMMaaannnaaagggeeemmmeeennnttt PPPrrraaaccctttiiiccceeesss fffooorrr DDDrrryyylllaaannnddd CCCrrroooppppppiiinnnggg SSSyyysssttteeemmmsss Wild Oats (Avena spp.) Wild oats are one of Australia’s most widespread and grass (Bromus spp.) however Brome grass has a costly weeds of dryland cropping systems (Figure 1). It tubular leaf sheath and hairy leaves whereas wild oats infests two thirds of all cereal growing properties in have a rolled leaf sheath with few hairs on the leaves. southern Australia and is ranked second only to annual ryegrass as the most problematic weed Origin and Introduction species (Kirby 2000). Infestations can cause yield losses of greater than 80% in wheat, contaminate Wild oats originated in Asia or the Mediterranean grain and host cereal diseases (Nugent, Storrie & region and were most likely introduced into Australia as Medd 1999). It is estimated wild oats cost Australian a contaminant of small grains (Nugent, Storrie & Medd grain growers in excess of $150 million every year in 1999; Kirby 2000). lost production, cost of control and contamination of grain (Anderson 2003). Distribution Wild oats are found throughout the winter grain growing regions of Australia. Most wild oat populations (about 80%) contain both A.fatua and A.ludoviciana (Cousens 2003) however Avena fatua is the dominant species in southern Australia, Avena ludoviciana is the dominant species in northern New South Wales and southern Queensland and Avena barbata is found predominantly on roadsides and in non-agricultural areas (Nugent, Storrie & Medd 1999). BIOLOGY AND ECOLOGY Wild oats are one of the most competitive grass weeds Figure 1. A mature Photo: J.D. Dodd and are near equal competitors with wheat. Avena fatua plant Competition with the crop begins soon after emergence with most of the yield loss occurring in the first 6 weeks. It has been estimated that an infestation KEY POINTS 2 as small as 20 plants/m can cause a yield loss of 10% • Use an integrated weed management (IWM) in a wheat crop yielding 2t/ha (Anderson 2003). program Yield losses are strongly influenced by the density of • Be vigilant with record keeping and paddock the infestation and the vigour of the crop, and are monitoring greatest when the wild oats emerge at the same time • Be aware of the new mode of action groups for as the crop. Wheat yield, tiller number and dry matter certain herbicides reduce in a linear pattern proportional to the length of time in which wild oats compete with the wheat crop. Therefore maximum yield benefits will be obtained when controlled early as early as possible even though Legislation small yield increases can occur after removal later in Wild oats are not declared noxious in the the season. Murrumbidgee catchment. Wild oats host a number of cereal pests and diseases Taxonomy including cereal cyst nematode (Heterodera avenae), root lesion nematode (Pratylenchus neglectus and P. Wild oats belong to the Poaceae family along with thornei), rhizoctonia (Rhizoctonia solani) and crown rot wheat (Triticum aestivum), barley (Hordeum vulgare) (Fusarium graminearum). They also host the bacteria and oats (Avena sativa). There are three species of that cause annual ryegrass toxicity (Rathayibacter wild oats in Australia- Avena fatua, Avena ludoviciana toxicus). (also known as Avena sterilis) and Avena barbata. Wild oats tend to grow in patches in a paddock and are Wild oats are also commonly known as black oats and found on most soil types from light to heavy textured bearded oats. They can be confused with Brome soils with a pH range of 4.5-9 (Nugent, Storrie & Medd 1999). Identification Seed bank The leaves of wild oat Wild oat seeds are relatively short lived having a half seedlings usually twist in an life of only 6 months. This means 75% of the seed anticlockwise direction as bank can diminish in 12 months and 99% in 2 years in opposed to wheat and barley the absence of new seed inputs (McGillion & Storrie (Figure 2). They have some 2006; Medd 1996). Seedbank decline generally follows hairs on their leaves, a large an exponential pattern with the greatest loss occurring ligule, no auricles and the in the first year (56-81%) (Figure 5) (Nietschke 1997). emerging leaf is rolled as Seeds rarely survive longer than 3 years and research opposed to folded. The has shown that persistent control for 3-5 years can seedlings are blue-green in virtually eradicate wild oats. However due to the prolific colour, especially when seed production of wild oats one season of poor stressed. Mature wild oat control can replenish the seed bank. Soil type also plants are up to 120cm tall. affects the seedbank as seedling recruitment and seedbank decline is greater in sandy soil compared to heavy soils. Photo: weedman.forsham.net.au Figure 2. Avena fatua seedling 120 Before flowering, it is very difficult to distinguish between the wild oat species. The spikelets of A. fatua 100 (Figure 3) hang from both sides of the floret and from only one side in A. barbata. The spikelet of A. 80 ludoviciana does not break up easily as it does in the other two species. Wild oat seeds can vary in colour from black to yellow and may have gold-brown hairs 60 (Figure 4). 40 Wild oat seed in the soil (%) soil the in seed oat Wild 20 0 0 5 10 15 20 25 Time (months) Figure 5. Persistence of wild oat seeds in the soil in the absence of seed input (adapted from Storrie et al. n.d.). Seed dormancy and germination Seed dormancy is relatively short lived in wild oat seeds that are on or near the soil surface. Dormancy Photo: Ian Lunt will be greater in buried seeds due to the cool, moist environment and lack of oxygen. Buried seeds may Figure 3. Avena fatua spikelet (Photo Ian Lunt). remain viable in the soil for up to 10 years however once brought to the surface these seeds will be released from dormancy and will germinate readily. Approximately 40% of the wild oat (A. fatua) seed bank germinates after opening rains and a further 30% later in the season (Nugent, Storrie & Medd 1999). Germination occurs from autumn to spring with the later, smaller cohorts producing enough seed to replenish the seed bank. Wild oats have a large germination window and will germinate in temperatures of 10-26.5°C. The emergence patterns of the three wild oat species differ slightly although this is unlikely to significantly impact on management. A. fatua germinates from Photo: Ian Lunt autumn to spring whereas A. ludoviciana germinates in Figure 4. Avena fatua seed (Photo Ian Lunt). winter to early spring (Medd 1996). A. barbata predominantly germinates after opening rains (Nugent, infestation can produce 20,000 seeds/m2 (McGillion & Storrie & Medd 1999). Storrie 2006). The number of seeds produced depends on weed density, crop density and vigour, time of The dormancy of wild oat seeds depends somewhat emergence, soil moisture, soil fertility and on the origin of the seeds. Primary seeds of each management. spikelet have been found to germinate in a single cohort following opening rains whereas secondary Most seeds of wild oats fall within one metre of the seeds are more persistent and therefore have parent plant. Long distance spread commonly occurs protracted germination (Cousens 2003). in fodder and grain, by livestock (e.g. on their coats) and on machinery. Delaying harvest until more seed Flowering has shed from the parent plant may reduce the dispersal of mature seeds by harvesters. The wild oat panicle is spreading and open, up to 40cm long and 20cm wide, and occurs on both sides of the stem (except in A. barbata). The large spikelets MANAGEMENT have 2-3 flowers (2-5 in A. ludoviciana) and the florets fall as single seeds when mature. A.ludoviciana The physiology of wild oats (staggered germination, flowers slightly earlier than A.fatua however the prolific seed production, self-pollination, high implications for management are likely to be competitiveness, rapid maturity and early seed shed) insignificant. together with widespread herbicide resistance makes their control difficult. It is essential to use an integrated Seed production and dispersal weed management (IWM) approach utilising a wide range of chemical, cultural and biological control Wild oats are self-pollinated so reproduction can occur options (Table 1). from a single plant. They are prolific seed producers and one plant can produce 225 seeds and an Table 1. Weed control tactics and their expected control for wild oats (Avena spp.) (McGillion & Storrie 2006). Tactic Likely control (%) (and control range) Crop choice and sequence 95 (30-99) Improve crop competition 70 (20-99) Herbicide tolerant crops 90 (80-99) Autumn tickle 40 (30-60) Knockdown pre-sowing (non-selective herbicide) 80 (70-90) Pre-emergent herbicides 80 (70-90) Selective post-emergent herbicides 80 (70-90) Spray-topping (selective herbicide) 90 (60-99) Pasture spray-topping 80 (70-90) Cutting for hay and silage 97 (95-99) Grazing 75 (60-80) Weed seed collection at harvest 70 (20-80) Reproduction rather than seed carryover is the main Integrated weed management programs should be mechanism of persistence in wild oat populations. based on long-term considerations including seed Management programs should aim to prevent seed production and the possibility of herbicide resistance production and seedbank inputs every year while developing. Jones, Cacho and Sinden (2003) minimising reductions in grain yield and quality. concluded that there are significant potential economic Infestations should be controlled as early as possible benefits associated with long term integrated weed after emergence as wild oats do most damage due to management systems for the control of wild oats and in competition early in the growing season (Table 2).